Once they get large enough, yes they will inflict damage to coral like they would stinging you. I do not think that they are predatory, it is just that it got a couple of pieces too many of mysid. For the most part, bristleworms of certain species, are great for your tank, as long as they stay about 2 inches and thin, not fat. You can set up a bristleworm trap which basically is like any insect container trap.
http://www.garf.org/news25p1.html
or you can buy one and this is the one I caught four with tonight
http://www.aquacave.com/detail.aspx?ID=932